1. The Field of the Invention
The present disclosure relates in general to the simultaneous imaging of different physical properties of an examined medium from the joint inversion of multiple datasets of physical field measurements, as occurs in geophysical exploration, nondestructive testing, and medical imaging.
2. The Related Technology
In resource exploration, it is uncommon for any single geophysical method to discriminate economic geology. Data from multiple geophysical surveys spanning gravity, magnetic, electromagnetic, and seismic methods are often interpreted to infer geology from models of different physical properties. In many cases, the various geophysical data are complimentary, making it natural to propose a formal mathematical framework for their joint inversion to a self-consistent, shared earth model.
Different approaches to the joint inversion of geophysical data have been discussed in the literature. The simplest case of joint inversion is where the physical properties of the earth model are identical between different geophysical methods, such as the joint inversion of a DC resistivity survey and a time-domain electromagnetic survey for a common conductivity model. In another case, joint inversion may infer theoretical, empirical or statistical correlations between different physical properties, such as statistical relations between the resistivity and seismic velocity to jointly invert electromagnetic and seismic data for a common rock physics model. In yet another case, the different physical properties are not correlated but nevertheless have similar structural constraints such as seismic and resistivity defining a hydrocarbon reservoir container, so joint inversion can be formulated as a minimization of the cross-gradients between different physical properties (Colombo et al., 2010, U.S. Pat. No. 7,805,250 B2).
Existing methods of joint inversion are inadequate for capturing geological complexity. For example, analytic, empirical or statistical correlations between different physical properties may exist for all or only part of the shared earth model, and their specific form may be unknown. As another example, structures that are present in the data of one geophysical method may not be present in the data of another geophysical method, such as a change in acoustic impedance and lack of a resistivity gradient across a change in lithological facies. As yet another example, there may exist any combination of analytic, empirical or statistical correlations with structural correlations between different model parameters and/or different attributes of the model parameters. There remains a requirement to develop a generalized method of joint inversion which would not require a priori knowledge about specific analytical or empirical or statistical relationships between the different model parameters and/or their attributes.